Dr Robert Mensah says sucking green mirids are difficult to control in both transgenic Bollgard and conventionally grown cotton - they are highly mobile, difficult to sample accurately and the source of the population is difficult to determine.

NSW Department of Primary Industries (DPI) researchers have come up with an environmentally friendly treatment for an insect emerging as one of the cotton industry’s biggest pests.

Since 2001, DPI principal research scientist Dr Robert Mensah has been working with two fungi which are showing great promise as a biological insecticide to control the insect, green mirid, in both transgenic Bollgard and conventional cotton crops.

This season, a large scale trial using a new formulation of the fungi has controlled green mirids to the same level as a commonly used chemical insecticide.

Chemicals used to control green mirids in the 2005-2006 season are estimated to have cost growers more than $11.7 million (average $38 per hectare), excluding application costs.

Of the State’s total planting for the 2005-06 season, 90 per cent was Bollgard cotton.

Dr Mensah says about 40 percent of all insecticides used on Bollgard cotton crops in the 2003-04 and 2004-05 seasons were to combat green mirids.

An adult green mirid infected by one of the fungi.

He said efficacy and performance of the fungal insecticide would improve with improved knowledge of formulation and application techniques.

One of the two fungi being tested is showing more promise, and this will be produced in large quantities and undergo large scale commercial trials in 2006-07, before being commercialised.

'Since the commercial release oftransgenic Bollgard cotton in 2003, sucking pests - particularly green mirids - have emerged as major pests,' he said.

'Green mirids are difficult to control because they are highly mobile, difficult to sample accurately and the source of the population is difficult to determine.

'They also seem to have few effective natural enemies.'

Dr Mensah said there was concern green mirids might develop resistance if the reliance on insecticides against green mirids continued at this rate.

'In addition, the insecticides applied against green mirids could also disrupt natural enemies and flare up other pests such as aphids and mites,' he said.

Dr Mensah and his colleagues at the Australian Cotton Research Institute at Narrabri screened 30 fungal isolates before narrowing down the most promising ones for field trials.

The fungi produce spores which, when applied to crops, either attack the insects directly or are picked up from the crop surface by the insect, and then germinate and invade its body tissue.

The insect dies within three to seven days.

Dr Mensah said a fungal insecticide was considered a bio-pesticide and hence did not affect the environment in the same way as synthetic insecticides.

'The use of the fungus will minimise or reduce the use of synthetic insecticides,' he said.

DPI’s northern farming systems research leader, Dr Bob Martin, said Dr Mensah’s work was a significant contribution to the department’s research strategy to reduce pesticide use in cropping systems but maintain productivity and profitability.

Contact: Dr Robert Mensah, NSW DPI, Narrabri, (02) 6799 1500 or robert.mensah@dpi.nsw.gov.au.

- JOANNE FINLAY

This story appears in Agriculture Today.